Hi guys, long time lurker but first time poster! I own a 2001 XJR and for the past 2-3 weeks while driving ASC & TSC would come on but when I restart my Jag it goes away. I went to the post office came home the light came on but didn't think much of it till I came out about an hour later, she started funny and then idled high and then the TSC, ASC, and failsafe appeared on my dash. I have no throttle response of course. so I ordered a brake light switch from ebay and plugged it in and still same deal. I have reset my computer and discharged my frame prior to the switch replacement. I have replaced the switch. I still have the same issue. I never used my cruise control but have hit the switch a few times on accident when attempting to select S mode. I have noticed thar the light on the cruise doesn't come on. It does for S mode though. Is there a way to check the switch? Do I need to reset my computer again after installing the switch? I'm super lost and I've tried not to try and ask the same questions but I need help please

 

Sounds like it's the throttle body, not the ABS or brake switch.

First things first, CHECK YOUR CODES!
If you have P0121 then you have a throttle position sensor error. You can get yours rebuilt through ASI, or a couple of other places I believe.
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Just idled to orileys and it looks like I got the P1229 code which it TB related... :-( any cheap quick fixes? Oh and I have a brake light switch if somebody needs it I got it for 25 plus shipping ill let it go for the same... Thx everybody!

Edit: the cruise red light still does not come on with the button on is this related?

 

How would I go about troubleshooting my TB and possibly fixing it without buying a new one? What should I check/do first? Thank you for all the help!

 

search on here for the fault codes, there aren't many problems we haven't seen before

 

The 2001 is an AJ27 engine, the throttle has 2 main electrical connectors that need checking. Jaguar offered a gold pin connector set upgrade you can buy from the dealer, as oxidization of these connector pins leads to all sorts of funny business. Try disconnecting and reseating them with wd40 or such first.
The cruise light will be a bulb failure they don't last forever. You can replace them but its a fair old job for the result.

 

First off thx Sean B. I did what you said and it definitely worked. Ok so here's the catch..... It was great it revved and idled but I bought some TB cleaner so I went to spray some to clean it up a little and then it died once I moved the air intake hose. So I went to restart her and she went back into failsafe mode :-( I went and reseated both connections again and it's still stuck in failsafe mode. Did I mess something else up or what just happened? It's now dark out and I have no more light to try everything again..... Is there something I did wrong or what would the other possibilities could be the reason for this happening after it died and tried to restart?

 

There is nothing wrong with the throttle body itself, it's the throttle position sensor on the side.

What did you do to get the spray in there? did you just take the cover off the airbox, or did you take something else off?

 

if you started the car or tried to run it without the intake snorkel then the car has no air metering as the MAF is at the other end!

Put it all back together, perform a hard reset, then go for gold.

 

Ok so I took the air intake tube to the throttle body to get to the 2 electrical connections and sprayed them with wd40 and applied dieelectric grease, didnt end up spraying tb cleaner into my tb (just mentioned that it died to see if there was something I did wrong to trip the failsafe again) So after all this I went to check it in the morning and it was in failsafe mode still. I then turned it off then back on as I pressed the gas upon initial start before system check had time to complete and it started and revved up fine. Ok so now its seems to be running fine but now the check engine light is on..... but yet runs great. Cycled the key a few more times and everything check out and no lights what so ever..... YAY Im going to drive my baby to work then, NOPE shes driving good then while doing 80 on the highway she goes into failsafe mode..... Pull over mess with the connections again then she was good. Drove for another mile or so and she does it again so I reseat both connections multiple times, press the gas when turning it on and then she worked again this happened 4 times then I finally made it to work. I and so sad and upset. I just want her to be ok. I dont want to regret my purchase but its getting harder and harder.

Oh also my cruise light is on when shes happy but when shes not its off?

 

Cruise control disables when you're in failsafe mode, thats normal (and sensible, when you think about it)

Have you checked out any of the other multitude of threads about tps failure yet?

Cleaning the contacts will only ever be a temporary fix at best. If you really want to fix it then either go talk to a mechanic, or ASI, and fix it properly.
You could look at buying a second hand tb assembly, but there are no guarantees you won't end up with the same issue in the future.

Ps if you're going to keep trying to fix it yourself you should really invest in an obd2 scanner. That way you can check Exactly what your fault codes and CEL are for

 

The whole cruise control does make sense. I have checked out other threads and it looks like I need to replace the connections with the gold connectors like stated by Jaguar and other fourm members that's what I've found so far. I do all my own work but only on the weekends because that's when I work on cars at my buddies shop but it's pretty far away. And he's a Chevy guy so he's no help so that's why I have you great people. I just was stressed a little. Thank you for all the help! Little by little I will get to know her like every other motor. But I'll tell you this she sure does have an attitude it's different but I like to learn...

 

There are a couple of reasons they fault, but it seems nobody ever really find out which issue it is. It could be the contacts, or there could be an issue inside the tps itself. I have just replaced my faulty TB with a rebuilt one from ASI. It would appear the contacts in the plug are fine, and the problem is inside the tps. The only real way to tell will be time though. Your car isn't a 99 model, so I believe you'll be better off getting yours rebuilt than spending an exorbitant amount on gold pins. Although I believe SNG Barratt can get them for you if that is the cause

 

your first job is to pull the codes posted by the CEL.

If they're P1121/1122 then it's a s/h throttle, the tps throttle position sensor cannot be replaced although we as forum members have chased hard for this part - also the tpps or throttle pedal position sensor.

Following my rebuild I had a persistent P1121 and only a replacement throttle fixed it. Depending on mileage, the higher it is the more likely you'll require another throttle, but it's worth exchanging the plug pins because whatever they cost its cheaper than a throttle - and if it turns out to be the throttle, at least you have it updated ready for the replacement tb.

Another thing that could be related, the cruise button, leave it off! The brake pedal lights switch located at the top of the brake pedal has 2 microswitches, with cruise on and you press the brake it turns it off in normal behavior, if the microswitch related to this function is faulty then a failsafe trips - so your test is to leave it off and see if it goes into failsafe, if it does again it's pointing at throttle tps, if not then blasting the switches with contact cleaner or changing the brake switch assembly is the next stage.
Hope this helps.

 

Thank you grandel & Sean B. I'll be sure to follow your guidance. You guys are awesome!

 

My memory is that the connections were fixed by the 2001 model year?

The problem is internal to the TPS. The Jag is a duel -- and the computers monitor both legs. If any anomalies are detected -- you get the warning. Obviously, the TPS is very important for the cruse control -- it can't trust the information if it senses a problem -- same for the traction. For whatever reason some of these have more problems - we and a lot with some ford V6's back in the mid 90's. Jaguar does not sell the part separately -- or this would be an easy fix.

The XJR uses a different TB. The fault can be very random -- and corrosion or dust can affect the small currents being detected. Try -- with the car off -- pushing the petal to the floor a few times -- do it 10 times. See what happens.

Mine gave me some issues about a year ago for a week -- I do the pedal push now occasionally - have not had the problem. Who knows?

Also - Don't clean the TB or move the internals .. if you do a search you will see TSB's regarding both.

 

another option is just to replace the TPS yourself
Hard to Find Jaguar XJ8 XK8 4 0L Throttle Position Sensor DENSO198500 3250 | eBay

I couldn't say for certain, but I have a feeling that this is all that ASI do when they rebuild the throttle bodies. Well, that and they give it quick sandblast to make it look clean again.
I would still recommend ASI due to the lifetime warranty though, meaning if you ever get the problem again they will fix it

 

Since none has come up with a source for the OE TPS - I can only assume that this was specific to the Jaguar V8 motor and was not an off the shelf part used in other vehicles.

It has been a while -- but I think that I remember seeing some back when they had the recall -- and they did not use screws to hold it in place. Does anyone know -- I have not looked at mine in a long time.

On most cars replacing the TPS is removing a couple of screws and putting the new one in ..

 

as above, you can just buy the TPS itself, and I'm sure you could fit it yourself, like this guy did...
She's Fixed! TPS Problem Resolved! | Jeeves and the Jaguar

 

I have an '01 R and fought the same symptoms with my car for a year and 1/2 checking for every other possible solution. I finally just pulled the trigger and bought a rebuilt TB from ASI. No more problems. Take your time when doing the exchange, and remember to use a new Jaguar OEM gasket underneath!